Japanese Patent Publication No. H04-355714A discloses that light waves and modulated waves are increased in interaction length by folding optical waveguides of an optical control element at an end surface of a substrate, and consequently, the driving voltage is made low and the velocity mismatch between the lightwaves and signal waves are compensated to realize the high-speed operation.
In “Highly Functional Hybrid Modules Using Low Loss Direct Attachment Technique with Planar Lightwave Circuit and LiNbO3 Devices” T. Yamada et al. “ISMOT-2005” pp.107-110, 2005, disclosed is that a PLC (Planar Lightwave Circuit) and an LN (LiNbO3) waveguide device are connected. Further, in Japanese Patent Publication No. 2005-173162A, disclosed is that the PLC and the LN waveguide device are connected, and that on this occasion, since mode field diameters of optical waveguides are different from each other between the two substrates, a tapered part for adjusting the mode field diameters is provided between the substrates.
In addition, in Japanese Patent Publication No. 2004-245991A, a so-called fixture structure is disclosed.